First off, they look ok to me, doubtful it's a zinc defeciency. More likely a minor ph issue.

But if you are going to worry, here's a couple of things to ponder before you fill-out the troubleshooting form: (available in my signature)

How are you testing your ph?
What's your water ph?
What brand and type of soil?
What kind of nutrients? (brand, dosages and schedule)